Improvement in manufacture of alum



UNITED STATES PATENT OFFICE.

GEORGE P. ROoKwELL, OF BALTIMORE, MARYLAND.

IMPROVEMENT IN MANUFACTURE OF ALUM.

Specification forming part of Letters Patent No. 196,043, dated October 9,1877 application filed September 24,1877.

Toall whom it may concern:

Be it known that I, GEORGE P. ROoKwELL, of the city of Baltimore, in the State of Maryland, have invented a new and useful Improvement in the Manufacture of Alum, of which I do hereby declare the following to be a full, clear, and exact description.

Myinvention relates, in general to that special division of the Various modes of alummanufacture in which alum, sulphate of alumina," and other aluminous compounds are made from such materials as contain, principally, alumina as a source of alum, and to which, consequently, sulphuric acid and alkaline salts have to be added, but has especial reference to that subdivision of the above class in which the mineral or earth employed has heretofore been shales or common clay.

For a fuller comprehension of my improvement it becomes necessary to set forth and contrast with the same the processes and materials heretofore in use in such subdivision of the manufacture.

In the class of manufacture of aluminous {CODlIJOlUldS to which .my invention relates it )is a prerequisite that some source of alumina {be had which is, as nearly as may be, unconltaminated by impurities, such as carbonate of lime or iron, which tend to impair the resultant product, and wherein the alumina exists in a condition to be readily dissolved by sulgphuric acid.

Heretofore, while such materials as cryolite, bauxite, and almninous shales have been employed, clay has been chiefly resorted to as the most desirable source of alumina.

Clay is a compound of silica and alumina, (forming silicate of i alinnina,) attended with more or less impurities.

The clays so called above are believed to have been of igneous origin. m

It is a well-known property of alumina that if exposed to a high heat it becomes difiicult, if not almost impossible, of solution in sulphuric acid. The alumina, then, of clay, having undoubtedly at some geologic period been exposed to a very high temperature, is to-day found to be so deficient in the requisite solubility as to cause its use in alum-manufacture to be attended with tedious and costly processes to obtain it in solution, as well as free it from the impurities common to it.

The process of making alum from clay consists, essentially, of the following steps, viz: Roasting of the clay, digestion with excess of sulphuric acid, dilution of the solution, separation of silica, evaporation, final addition of alkaline equivalent, and recrystallization.

It is clearly obvious that a process such as that described, being tedious and requiring the use of much apparatus, is costly, while it is attended with considerable loss of alum product, for the reason that, owing to the insolu: bility of clay, only about one-half its aliunina is obtained in the form of alum; also, a large portion of the liquid in the crystalline solu- I have discovered that alum and aluminous compounds can be more cheaply and advanl after set forth, by the employment, as a source of alumina, of a material never heretofore used for such p1n-poseto wit, the mineral Indianaite, which is a comparatively pure and readilysoluble silicate of alumina. It is of approximately the following composition, as set forth in the annexed analyges tageously manufactured, in the manner hereink B C D Silica 45.90 47.05 47.13 42.28 Alumina 40.34 37.14 36.76 43.05 Water 13.26 15.55 15.13 14.66 Lime and magncsia Trace .03 .04 Trace Oxide of iron Trace Trace Manganese .03 Trace See p. 306, vol. 10, American Journal of Science and Arts, 1875.]

This mineral undoubtedly results from decomposition by aqueous action, to which origin may be attributed its wonderful solubility in sulphuric acid. Its peculiar fitness for alum manufacture is witnessed by the fact that the ahunina present in it may be extracted by treatment even with cold sulphuric acid, the quantity required being but about the arid equivalent to the alumina present; clay, on the contrary, requiring the sulphuric acid in large excess.

Heretofore, in the manufacture of alum from kaolins, the application of heat to eflect solution has been indispensable requisite, while in my process, as stated, it may be omitted The Indianaite is also practically free from iron and the other objectionable impurities found in clay.

This mineral is not to be confounded with the anorthites or silicates of alumina and lime, ofi which one variety is termed Indianite, fnolm the fact that it is abundantly found 111 India. Indianaitemayreadilybedistinguished by its ccmposition, being a practically pure silicate of alumina, by its fracture and adhesion to: the tongue.

A process convenient for the production of ahmt from lndianaiteis the following: First, mix the desired quantity of Lndianaite-with about the equivalent of sulphuric acid (preferat about 40- Baum) tothe alumina pres-- cut. When the reaction of the above admixtune. has become complete, add sufiicient water.

Instead of adding water, as above stated, it may be permitted to harden, and then be imeaetedwitlrwater or the crude cake so formed may be directly sent into commerce.

By this means sulphate of alumina isobtained insolutions, the insoluble silica settling tained, it is evident that there results little or no impure mother-liquors to recrystallize or to run to waste and cause loss.

It is obvious that the Indianaite may be applied with equal advantage, in the manufac ture of other aluminous compounds used in the arts and trades, such as sulphate alumina, alum-cake, &c.

Having thus deseribedimy invention, 1 claim and desire to secure by Letters Patent 012' the United States- 1. The process herein: described for the manufacture ofi aluminicsulphate, the same consisting in the decompositionofi the mineral Lndianaite by means of sulphurieacid, elimination of separated silica, andv crystallization, substantially as set forth.

The process herein describedfor the manufacture of alum, the same consisting, in

- the decomposition of? the mineral Indianaite by means of sulphuric acid, elimination of separated silica, addition: of the equivalent of alkali, and. final crystallization-,.alh substantially as set forth.

P2 RIDEKWEEL.

Witnesses CON-RAJ) SEMPER, W. W. DoUGHER'rY. 

